QUANTICO, Va. — As the Marine Corps transitions from 14 years at war back to an expeditionary force capable of worldwide crisis response, its aviation arm is undergoing a near-total transition to more capable platforms, if not outright replacing entire fleets of legacy aircraft.

Current budget uncertainty and ongoing delays in development and delivery of next-generation aircraft have put a premium on keeping legacy aircraft up-to-date and technologically relevant until platforms like the F-35B and CH-53K King Stallion heavy lift helicopter come online in sufficient numbers, Col. Paul Fortunato, director of Marine Corps aviation weapons systems requirements, said Sept. 23.

“It’s critically important that we have the money, the support from the Hill and support from industry to help with that efficient, timely transition,” he said at the Modern Day Marine technology expo.

The service is in the process of upgrading or replacing its C-130 tanker/transports, the V-22 Osprey, H-1 utility and attack helicopters and the AV-8B Harrier jump jet. It has begun fielding operational F-35B short-takeoff and vertical-landing jets and is set to begin flight testing of the largest military helicopter in the world, the CH-53K King Stallion.

“We are in the middle of transitioning every platform in Marine aviation,” Fortunato said. “Until the transition is complete, it is vital that the Marine Corps, in partnership with industry “ensure that legacy aircraft and platforms remain relevant.”

The service already has upgraded about two-thirds of its C-130 fleet to the most modern version, the C-130J, he said. The Marine Corps plans to buy at least 79 C-130Js.

Marine Fighter Squadron VMF-121, based at Yuma, Ariz., became the first operational F-35B squadron in July and pilots are just now figuring out how the platform can and will be used in future fights. The jet has been tested but not yet deployed on amphibious warships, where it will eventually take the AV-8B’s place.

Half of the Marines’ H-1 family of helicopters have been upgraded or replaced with more capable models. Introduction of the twin-engine, four-bladed UH-1Y is nearly complete and replacement of the AH-1 Cobra with the AH-1Z Viper is in the early stages, Fortunato said.

The Marines also have taken delivery and fielded about two-thirds of its required fleet of V-22s, which give deployed forces vastly greater range and speed over conventional rotorcraft. The aircraft has a 450-mile combat radius, which can be more than doubled if a tanker is available for mid-air refueling, Deputy Commandant for Aviation Lt. Gen. Jon Davis noted.

“V-22 is one of the things that we bought and have adapted for the Marine Corps that has changed the way we do business,” Davis said. “The number one thing that would bother me if I was a bad guy is an amphibious carrier with a squadron of V-22s on board.”

The service plans to outfit the MV-22 with its own onboard aerial refueling system so the aircraft can transfer fuel to other V-22s, other helicopters and even F-35s. That capability is funded in the service’s fiscal year 2016 budget request and should begin fielding in 2017. Plans also are in the works to increase the Osprey’s weapons load with forward-firing missiles and rockets, among other lethality enhancements.

Aircraft like the Harrier need survivability, lethality and interoperability upgrades to remain operationally relevant until the F-35B is fielded in greater numbers, he added. Plans are to add degraded visual environment equipment in legacy aircraft along with enhanced precision weapons systems, missile warning systems and Link-16 communication nodes on Harriers. Legacy platforms also need engine, power, structural and electrical system upgrades, he said.

Ongoing delays in the development of the CH-53K demonstrate the problem. With initial operational capability now pushed to 2019, the aging CH-53E must also remain in service for another decade at least. The King Stallion has yet to take its maiden flight because of structural deficiencies found during ground testing. Davis has said that first flight will take place before the end of the year for the King Stallion, which will triple the lift capability of the CH-53E. The service eventually will buy 200 CH-53Ks.